OK, I've had GSD3's fitted today for £412 all around, balanced, new valves etc.
Early feedback is that they're a massive improvement over what I had previously, though of course they still need to be scrubbed in. I did have them spinning a little as the roads are wet and slippery around here but I noticed that the ESP handled it much better than it did with the cheapo unmatched pair on the front.
So far I'm very happy and glad I picked these tyres. I guess only time will tell whether I made the right decision long term.
Thanks for all the input guys